For 1, suppose that x is irrational, that p is rational and q = p - x. Either q is rational or irrational. If q is rational then p - q is rational which would imply that x is rational. By contradiction, then p - x must be irrational. Therefore x + q = p, implying two irrational numbers can sum to a rational number.

For 2, how about -3, -1 and 1.

For 3, 3 is the only example. One less than a square is n ^ 2 - 1 = (n+1)(n-1). For n=2 the answer is 3 (3*1). For n > 2 the result is clearly factorable into two numbers > 1.